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| United States Patent |
5,711,178
|
|
Hogendoorn
, et al.
|
January 27, 1998
|
Die for use in die-necking of a metal can body and method using such a
die
Abstract
A die for use in a stage of a multi-stage die-necking process of a metal
body such as a beverage can, has a surface around a center-line. The die
surface, seen in longitudinal section through the center-line, has a
profile which includes in direct succession a feed-in zone, an
intermediate zone and a neck zone. The intermediate zone has, as well as a
contact part, a relatively steep part in which tangents to the die surface
include an angle .alpha. to the center-line greater than .alpha..sub.n,
where .alpha..sub.n is the neck angle between the necked part following
die-necking and the center-line of the body. The presence of this
non-contact steep part reduces the axial force needed in the die-necking.
| Inventors:
|
Hogendoorn; Auke (Heerhugowaard, NL);
Louwerse; Gerard M. (Velserbroek, NL);
Schaaper; Hans N. (Heemskerk, NL)
|
| Assignee:
|
Hoogovens Staal BV (Ijmuiden, NL)
|
| Appl. No.:
|
668475 |
| Filed:
|
June 25, 1996 |
Foreign Application Priority Data
| Current U.S. Class: |
72/352; 72/348 |
| Intern'l Class: |
B21D 022/00; B21D 022/21 |
| Field of Search: |
72/348,349,352,354.6,356,379.4
413/69
|
References Cited
U.S. Patent Documents
| 3771476 | Nov., 1973 | Heinle | 72/350.
|
| 3964413 | Jun., 1976 | Saunders.
| |
| 3995572 | Dec., 1976 | Saunders.
| |
| 4403493 | Sep., 1983 | Atkinson | 72/352.
|
| 5355710 | Oct., 1994 | Diekhoff | 72/379.
|
| Foreign Patent Documents |
| 0020926 | Jan., 1981 | EP.
| |
| 4-9232 | Jan., 1992 | JP | 72/379.
|
| 8403873 | Oct., 1984 | WO.
| |
Other References
European Search Report, Feb. 29, 1996.
|
Primary Examiner: Larson; Lowell A.
Assistant Examiner: Butler; Rodney
Attorney, Agent or Firm: Watson Cole Stevens Davis, P.L.L.C.
Claims
What is claimed is:
1. Die for use in a stage, other than a first stage, of a multi-stage
process of die-necking of a metal can body, which die has a centre-line
and an internal die surface extending around said centre-line for
contacting a part of said can body which is being necked by relative
movement of said can body and said die surface in a direction parallel to
said centre-line, said die surface having, as seen in a longitudinal
section including said centre-line, a profile comprising in direct
succession
a feed-in zone,
an intermediate zone, and
a neck zone,
said feed-in zone having a spacing from said centre-line corresponding to
the dimension of said can body at a non-necked part thereof adjacent the
part being necked,
said neck zone having a spacing from the centre-line corresponding to a
desired neck size of a necked part of said can body after its die-necking
in the die, and
said intermediate zone having, as seen in said longitudinal section
including said centre-line, a contact surface part which has tangents at
non-zero angles to said centre-line and which in use contacts said can
body to shape the can body, and at a location between said contact surface
part and said feed-in zone, a relatively steep surface part which has
tangents that extend at an angle .alpha. to said centre-line greater than
a maximum angle .alpha..sub.n between said tangents of said contact
surface part and said center-line of tangents to said contact surface part
relative to said centre-line.
2. Die according to claim 1 wherein .alpha..gtoreq.40.degree..
3. Die according to claim 1 wherein tangents at said contact surface part
extend at a maximum angle of 30.degree. to 40.degree. to said centre-line
of the die.
4. Die according to claim 2 wherein .alpha..gtoreq.50.degree..
5. Die according to claim 4 wherein .alpha..gtoreq.60.degree..
6. Die according to claim 5 wherein .alpha..gtoreq.70.degree..
7. Die according to claim 6 wherein .alpha..gtoreq.80.degree..
8. Die according to claim 7 wherein .alpha..gtoreq.90.degree..
9. Die for use in a stage, other than the first stage, of a multi-stage
process of die necking of a metal can body, which die has a centre-line
and an internal die surface extending around said centre-line for
contacting a part of said can body which is being necked by relative
movement of said can body and said die surface in a direction parallel to
said centre-line, said die surface having, as seen in a longitudinal
section including said centre-line, a profile comprising in direct
succession
a feed-in zone,
an intermediate zone and
a neck zone,
said feed-in zone having a spacing from said centre-line corresponding to
the dimension of said can body at a non-necked part thereof adjacent the
part being necked,
said neck zone having a spacing from said centre-line corresponding to a
desired neck size of a necked part of said can body after its die-necking
in the die, and
said intermediate zone having, as seen in said longitudinal section
including said centre-line, a contact surface part which has tangents at
non-zero angles to said centre-line and which in use contacts said can
body to shape the can body, and at a location between said contact surface
part and said feed-in zone, a second surface part which has tangents that
extend at angles .alpha. to said centre-line which are not less than
40.degree. and are greater than the maximum angle between said tangents of
said contact surface part and said centre-line.
10. Die according to claim 9 wherein .alpha..gtoreq.50.degree..
11. Die according to claim 10 wherein .alpha..gtoreq.60.degree..
12. Die according to claim 11 wherein .alpha..gtoreq.70.degree..
13. Die according to claim 12 wherein .alpha..gtoreq.80.degree..
14. Die according to claim 13 wherein .alpha..gtoreq.90.degree..
15. Method of die-necking a metal can body to provide a neck thereon
comprising the steps of (a) positioning an open end of a metallic can body
within an initial die having an internal die surface extending around a
centre-line thereof and moving said can body relative to said first die to
begin formation of a necked part of said can body, and subsequently (b)
positioning the necked part of said can body within a subsequent die
having an internal die surface extending around a centre-line thereof and
moving said can body relative to said subsequent die to continue formation
of a necked part of said can body, said subsequent die as seen in a
longitudinal section including said centre-line, comprising an internal
die surface profile defining in direct succession a feed-in zone, an
intermediate zone and a neck zone, said feed-in zone having a spacing from
said centre-line corresponding to the dimension of said can body at a
non-necked part thereof adjacent the part being necked, said neck zone
having a spacing from said centre-line corresponding to a desired neck
size of the necked part of said can body after step (b), and said
intermediate zone being a shoulder-shaped zone having a contact surface
part which contacts said can body to effect reshaping thereof and, at a
location between said contact surface part and said feed-in zone, a
relatively steep surface part which, as seen in said longitudinal section
including said centre-line, has tangents that extend at an angle .alpha.
to said centre-line greater than an angle .alpha..sub.n which is the
maximum angle between said necked part of said can body and its
centre-line after the die-necking of said can body in the subsequent die
in step (b).
16. Method according to claim 15 wherein said can body is made of packaging
steel and its circumference at its necked part is reduced more than 39 mm
in not more than twelve of said die-necking stages.
17. Method of die-necking of a metal can body to provide a neck thereon
comprising, the steps of (a) positioning an open end of a metallic can
body within an initial die having an internal die surface extending around
a centre-line thereof and moving said can body relative to said first die
to begin formation of a necked part of said can body, and subsequently (b)
positioning the necked part of said can body within a subsequent die
having an internal die surface extending around a centre-line thereof and
moving said can body relative to said subsequent die to continue formation
of a necked part of said can body, said subsequent die as seen in a
longitudinal section including said centre-line, comprising an internal
die surface profile defining in direct succession a feed-in zone having a
spacing from said centre-line corresponding to the dimension of said can
body at a non-necked part thereof adjacent the part being necked, said
neck zone having a spacing from said centre-line corresponding to a
desired neck size of the necked part of said can body after step (b), and
said intermediate zone being a shoulder-shaped zone having a contact
surface part which in step (b) contacts said can body to effect re-shaping
thereof, said intermediate zone further having, between said contact
surface part and said feed-in zone, a non-contact surface part which
remains out of contact with said can body during the movement of said can
body relative to said subsequent die in step (b).
18. Method according to claim 17 wherein said can body is made of packaging
steel, and its circumference is reduced at its necked part by more than 39
mm in not more than twelve of said die-necking stages.
19. Die according to claim 18 wherein tangents at said contact surface part
extend at a maximum angle of 30.degree. to 40.degree. to said centre-line
of said die.
Description
FIELD OF THE INVENTION
This invention relates to a die for use in a stage, other than the first
stage, of a multi-stage process of die-necking of a metal can body, such
as a beverage can body. The invention further relates to a method of
die-necking of a metal can body in a plurality of die-necking stages using
such a die.
DESCRIPTION OF THE PRIOR ART
A drinks or beverage can body commonly is formed as a one-piece drawn
seamless tubular body having one end open for filling, prior to the
attachment of the lid. To permit the lid to be attached, it is known to
reduce the diameter of the can body adjacent the open end, i.e., to neck
the can body. The can body is usually cylindrical, but the invention is
not limited to this shape.
In this context necking is understood to be the process called die-necking,
wherein the body being made is moved into a die with the end to be necked
leading, which die is of such a shape that the neck size on the neck end
is reduced. During die-necking the body is supported internally by
applying into it an internal overpressure, and the neck is supported
internally by a support element. The necking process is carried out in
more than one stage, whereby a neck is formed on the body in a number of
stages. By supporting the material at the neck the force to be exerted
axially on the body for necking becomes increasingly greater, and in the
last stages approaches the critical limit at which the body can still
produce the axial force. In order to reduce the neck size as much as
possible without damaging or collapsing the body, the shape of the body,
particularly of its base, is optimized in order to enable this high force
to be withstood successfully.
An example of such a known die is disclosed in U.S. Pat. No. 5,355,710. The
die has an internal die surface around a centre-line. This internal
surface has, as seen in a longitudinal section through the centre-line, a
die profile which comprises in direct succession a feed-in zone, an
intermediate zone and a neck zone. The radial spacing from the centre-line
of the feed-in zone corresponds to the relative dimension of the body in
the non-necked area bordering the necked part of the body, and the radial
spacing of the neck zone corresponds to the desired neck size of the neck
of the body. The intermediate zone has a shoulder shape with tangents to
the die-shell surface at an angle to the centre-line corresponding to the
neck angle between the necked part following die-necking and the
centre-line of the body. It appears that, at least at the end of the
stroke, i.e., the end of the movement of the can body into the die, the
can body contacts the whole length of the intermediate zone, between the
feed-in zone and the neck zone.
Similar dies are shown in WO-84/03873 and EP-A-20926. Dies which do not
have a feed-in zone contacting and supporting the can body are also shown
in EP-A-20926 and in U.S. Pat. No. 3,995,572.
SUMMARY OF THE INVENTION
The object of the invention is to provide a die, and a method for
die-necking of a can body, which reduces the axial force which occurs in
necking. In this aim, the invention deviates from the prior practice, in
which it has been sought to strengthen and/or support the can body so that
it can resist the axial force.
The invention lies in providing a second portion of the intermediate zone
of the die, between the contact portion and the feed-in portion which also
contacts the can body, the second portion having tangents at a steeper
angle (.alpha.) to the centre-line than the contact portion. In the
method, this second portion remains out of contact with the can body, even
at the end of the stroke. By this means it appears that the axial force
can be substantially reduced, even by as much as several tens of percents.
Alternatively, the same size reduction of the necked portion can be
carried out in fewer necking stages, or a greater size reduction can be
achieved in the same number of stages. This permits increased capacity
and/or reduces costs.
According to the invention in a first aspect, there is provided a die for
use in a stage, other than the first stage, of a multi-stage process of
die necking of a metal can body. The die has a centre-line and an internal
die surface extending around the centre-line for contacting a part of the
can body which is being necked by relative movement of the can body and
the die surface in a direction parallel to the centre-line. The die
surface has, as seen in a longitudinal section including the centre-line,
a profile comprising in direct succession
a feed-in zone,
an intermediate zone and
a neck zone.
The feed-in zone has a spacing from the centre-line corresponding to the
dimension of the can body at a non-necked part thereof adjacent the part
being necked. The neck zone has a spacing from the centre-line
corresponding to a desired neck size of a necked part of the can body
after its die-necking in the die. The intermediate zone has, as seen in
the longitudinal section including the centre-line, a contact surface part
which has tangents at non-zero angles to the centre-line and which in use
contacts the can body to shape the can body, and at a location between the
contact surface part and the feed-in zone, a relatively steep surface part
which has tangents at an angle .alpha. to the centre-line greater than an
angle .alpha..sub.n which is the maximum angle between the necked part of
the can body and its centre-line after the die-necking of the can body in
the die.
The invention further provides a die, having a feed-in zone and a neck zone
as described above, and an intermediate zone between them. The
intermediate zone has, as seen in longitudinal section including the die
centre-line, a contact surface part which has tangents at non-zero angles
to the centre-line and which in use contacts the can body to shape the can
body, and at a location between the contact surface part and the feed-in
zone, a second surface part which has tangents at angles .alpha. to the
centre-line which are not less than 40.degree. and are greater than the
maximum angle between the tangents of the contact surface part and the
centre-line.
In another aspect, the invention provides a method of die-necking a metal
can body to provide a neck thereon comprising performing a plurality of
die-necking stages in which a part of the can body is progressively
reduced in circumference. The method includes, in at least one of the
die-necking stages, moving the can body relative to a die having an
internal die surface extending around a centre-line and having, as seen in
a longitudinal section including the centre-line, a profile comprising in
direct succession a feed-in zone, an intermediate zone and a neck zone.
The feed-in zone has a spacing from the centre-line corresponding to the
dimension of the can body at a non-necked part thereof adjacent the part
being necked, and the neck zone has a spacing from the centre-line
corresponding to a desired neck size of a necked part of the can body
after its die-necking in the die. The intermediate zone is a
shoulder-shaped zone having a contact surface part which contacts the can
body to effect re-shaping thereof and, at a location between the contact
surface part and the feed-in zone, a relatively steep surface part which,
as seen in the longitudinal section including the centre-line, has
tangents at an angle .alpha. to the centre-line greater than an angle
.alpha..sub.n which is the maximum angle between the necked part of the
can body and its centre-line after the die-necking of the can body in the
die.
The invention also consists in the use of a die of the invention as
described above, in a stage of a multi-stage die-necking process.
By the method according to the invention, when the can body is made of
packaging steel, its circumference at its necked part can be reduced more
than 39 mm in not more than twelve of the die-necking stages.
Relative to a conventional can shaping process, the concept of the
invention typically means an angle .alpha..gtoreq.40.degree.. Although the
effect of reducing the axial force required may already occur at an angle
.gtoreq.40.degree., it is preferable and it is quite possible that the
angle may be made even greater, for example .gtoreq.50.degree.,
.gtoreq.60.degree., .gtoreq.70.degree., 80.degree., or even
.gtoreq.90.degree..
It can occur that the neck part formed in a preceding stage does not feed
well into the following die. This problem is rectified in the invention in
that the relatively steep part of the die is situated between the feed-in
zone and the contact part near to the contact part. The contact part is a
part of the die profile at which during the movement the body first comes
into contact with the die surface. Due to a spring-back effect, this
contact part will typically be on a somewhat greater radius than the neck
zone in the last preceding stage. It is preferable for tangents to the die
surface in the contact part to include a maximum angle .beta. to the
centre-line between 30.degree. and 40.degree..
By making any contact impossible at the relatively steep zone, it is found
that friction is reduced, while surprisingly by modifying the die profile
for the die part in question, no particular disadvantages are found to
arise in respect of process operation or product quality in general and
the neck shape in particular.
BRIEF INTRODUCTION OF THE DRAWINGS
The invention will now be illustrated by non-limitative embodiments which
are described below and are shown in the accompanying drawings, in which:
FIG. 1 shows the die-necking process schematically;
FIG. 2 shows a cross-section of a die in accordance with the state of the
art;
FIG. 3 shows a cross-section of a die in accordance with the invention
intended for a fourth necking stage of a body of packaging steel of 66 mm
diameter;
FIG. 4 shows a die cross-section of a die in accordance with the invention
for a fifth necking stage following the fourth necking stage carried out
in the die of FIG. 3;
FIG. 5 shows a die in accordance with the invention for a subsequent sixth
necking stage after the die of FIG. 4;
FIG. 6 shows a die in accordance with the invention for a subsequent tenth
necking stage in the same multi-stage process; and
FIG. 7 shows in a graph the axial forces in the necking stages using dies
of the conventional shape and dies in the shape in accordance with the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIGS. 2 to 6 have the relevant dimensions of the die in mm, which can be
read from the figures by the expert.
FIG. 1 shows a circle-cylindrical body of a beverage can which is
positioned with its base against a punch 3. By moving punch 3 in the
direction of die 1, a neck is formed at the end of the body which comes
into contact with the die 1. The neck is supported on the inside by
support element 2, also called a knock-out. A fluid can be supplied
through a duct (not drawn) extending through the support element 2 for
enabling the interior of the body to be pressurized in order to withstand
the forces exerted on the body during necking. This process is
conventional and need not be described here in detail.
FIG. 1 also shows a force sensor 4 which is used for sensing the axial
force exerted by punch 3 on the base of the body.
FIG. 2 shows the die profile of a die for a first necking stage in
accordance with the state of the art. In accordance with the state of the
art, the profile shape shown is also given to the dies for the subsequent
necking stages, but with a reduced radius at the neck zone for each
necking stage. Moreover, in necking in accordance with the invention, at
least the first necking stage, and possibly also a small number of
subsequent necking stages, are carried out with a die in accordance with
the state of the art.
As FIG. 2 shows, the die profile has a feed-in zone (at diameter 66 mm)
which contacts and supports the can body at its non-necked part, and a
neck zone (at diameter 64.30 mm) which contacts the necked-down part of
the can body. Both of these zones in the dies here illustrated are
parallel to the die centre-line, but either or both of them may
alternatively be slightly tapered (the feed-in zone tapering inwardly in
the feed-in direction of the can body and the neck zone tapering outwardly
in this direction). Between the feed-in zone and the neck zone is an
intermediate zone of curved shoulder profile at which the can body is
given its correspondingly curved shoulder. At the end of the stroke, the
entirety of the intermediate zone contacts the can body.
After the first necking stage is carried out, it is now advantageous to
carry out other necking stages using the dies in accordance with the
invention.
FIG. 3 shows the die profile of such a die in accordance with the
invention, intended for the fourth necking stage of such a die-necking
process, of a can body of diameter 66 mm. Along the profile from bottom to
top there is a feed-in zone at a diameter 66 mm which along a rounding of
radius 1 mm transfers into a steep part with an angle .alpha. of about
80.degree. to the die centre-line. This transfers by another rounding of
radius 1 mm into the contact zone having an angle .beta. of about
37.degree.. This transfers via a rounding of radius 4 mm into the neck
zone at a diameter 61.3 mm. Unless otherwise indicated, all dimensions in
the text and figures are given in mm. Thus, on the side of the contact
zone remote from the neck zone there is an indentation or recess which can
clearly be seen forming the relatively steep part of the profile. At this
indentation or recess, there is no contact with the can body, even at the
end of the movement of the can body into the die, in the necking stroke.
FIGS. 4, 5 and 6 show respectively profiles for a fifth, sixth and tenth
stage of this die-necking process in accordance with the invention.
In each of the dies of FIGS. 4 to 6, the maximum angle .beta. at the
contact surface part is 37.degree. to the die centre-line. This is the
region of initial contact of the can body with the die in the necking
stroke. Between this part and the feed-in zone there is, as in FIG. 3, a
recessed surface part at which there is no contact with the can body. This
recessed part has tangents at angles .alpha. substantially greater than
.beta.; in FIG. 4 the maximum angle .alpha. is 80.degree., in FIG. 5 the
maximum angle .alpha. is 85.degree. and in FIG. 6 the maximum angle
.alpha. is 90.degree..
In FIG. 7 the vertical axis expresses the highest axial force in kN exerted
by punch 3 on the body and the horizontal axis expresses the necking stage
number in the multi-stage necking processes. The force sensor 4 shown in
FIG. 1 is used to determine the highest force occurring in each of the 13
necking stages. The first three necking stages are carried out with
identical dies in the two processes, the highest forces occurring as shown
by the unbroken line. From necking stage four the dotted line shows the
forces measured when using dies in accordance with the invention as
illustrated in FIGS. 3 to 6 for stages four, five, six and ten, and the
continuous line shows the forces measured when using dies in accordance
with the state of the art, that is to say dies of a profile shape
displaying similarity to those shown in FIG. 2. The dashed/dotted line in
FIG. 7 indicates a critical limit at which there is a risk of a body of
packaging steel collapsing, namely at 2.71 kN in the case illustrated. It
can be clearly observed that a substantial reduction of the axial loading
of the body can be achieved by the invention, by an amount of over 500N.
In an embodiment of the invention, a can body of diameter 66 mm has reduced
in diameter at its neck portion, using dies such as shown in FIGS. 3 to 6,
to 53.3 mm in twelve steps, a circumference reduction of 39.9 mm.
It will be clear that the shape of the body is not limited to a purely
circle cylindrical shape, but could also be, for example, a rounded-off
square or elliptical shape. Although the results in FIG. 7 relate to
packaging steel, in the invention the body material is also not limited to
steel.
The invention also makes it possible to arrive at can bodies which may be
sealed with yet smaller lids.
Although embodiments have been described for explanation and illustration,
the invention is not limited to them but includes modifications and
improvements within the scope of the inventive concept herein disclosed.
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